The present invention relates to a device intended to provide a satisfactory lubrication in a mechanical rotary coupling which, for the particular installation conditions, can not be effectively lubricated in the known ways. A typical example of such a coupling is the one between the piston pin and the holes formed in the bosses of a piston for internal combustion engines. This coupling is such that the lubrication is effected only by the oil sprays reaching the piston pin surface by passing between the piston bosses and the connecting rod, and then penetrating the coupling to be lubricated. The operating conditions are further made more difficult in that the relative movement occurs within a very limited angle between stopping and reversing positions of the reciprocating motion, and under a high load, with consequent possible seizure phenomena. Attempts have been made till now to improve the operating conditions of such couplings, by means of such an exact machining as to minimize their surface roughness, but this measure has proved insufficient.